Methods, materials, and equipment useful in chemical-mechanical processing (CMP), which includes methods of polishing or planarizing a substrate, are highly varied, and are capable of being used to process a wide range of substrates having different surfaces and end uses. Substrates that are processed by CMP methods include optical products, semiconductor substrates, and other microelectronic device substrates, at any of various stages of fabrication. A wide range of CMP apparatuses, slurries, polishing pads, and methods are well known, with new products being developed on a continuing basis. Various liquid compositions (also known as polishing slurries, CMP slurries, and CMP compositions) are designed to process a surface of a semiconductor substrate when used with a pad to abrade the surface.
Particularly with advanced nodes of semiconductor processing, methods for processing surfaces that contain both tungsten and dielectric material have become especially important. In steps of preparing functioning structures from the tungsten, the substrate can begin with a discontinuous surface having patterned non-tungsten (e.g., dielectric) material having three-dimensional spaces such as channels, holes, gaps, trenches, and the like, that require filling with tungsten. The tungsten can be deposited over the discontinuous surface in a manner that not only fills the spaces, but, to ensure complete filling of the spaces, also produces a continuous layer of excess tungsten over the surface. The excess tungsten is then removed to expose a surface of the original patterned material with tungsten features deposited into the spaces between the patterned non-tungsten (e.g., dielectric) material.
An example of a substrate that has tungsten features disposed between dielectric features is the type of semiconductor substrate that includes tungsten “plug” and “interconnect” structures provided between features of dielectric material. To produce such structures, tungsten is applied over a surface that contains a patterned structure made at least in part from dielectric material, e.g., silicon oxide. The patterned dielectric surface is structured, i.e., non-planar, meaning that it includes a surface that is substantially flat or planar except for being interrupted and made discontinuous by the presence of the spaces such as channels or holes. When tungsten is applied to the structured dielectric-containing surface, the spaces are filled with the tungsten and a continuous layer of excess tungsten is formed over the surface. In a next step, the excess tungsten is removed by CMP processing to expose the underlying dielectric layer and to produce a planar surface of the tungsten disposed between the spaces of the dielectric material.
By some methods, tungsten is removed in a single step that uncovers the dielectric surface. By other methods, a “two-step” process can be used. In a first step a large portion of the excess tungsten is removed but the dielectric layer is not exposed. This step is commonly referred to as a “bulk” removal step during which a high tungsten removal rate is desired. A subsequent (second) step can be used to remove the remaining tungsten and expose the underlying dielectric and tungsten surface. This step is sometimes referred to as a “polishing” step, wherein a high tungsten removal rate may be important, but wherein other performance requirements are important too.
A polishing slurry may contain chemical ingredients selected specifically for processing a certain type of substrate, such as for polishing a tungsten-containing surface as opposed to a different surface that does not contain a metal or that contains a metal that is different from tungsten. Examples of such chemical ingredients include chemical catalysts, chemical stabilizers, inhibitors, surfactants, oxidants, and others. Each of these separate ingredients may be selected to improve desired processing of (e.g., efficient removal of) a material at a surface of a substrate. In addition, the CMP processing composition typically contains abrasive particles. The type of abrasive particles may also be selected based on the type of substrate being processed. Certain types of abrasive particles may be useful in polishing a tungsten-containing substrate surface but may not be useful for processing other CMP substrate surfaces.
Metal-containing catalysts, e.g., as provided by soluble metal-containing salts that dissociate in a liquid (e.g., aqueous) medium to produce a metal cation, have been used in CMP processes for removing tungsten from a substrate surface, in the past. The metal salt dissociates in the liquid to produce a metal cation that act as a catalyst, increasing the removal rate of tungsten, especially in the presence of an oxidizing agent. The metal cation facilitates formation of tungsten oxide at the substrate surface, which is then removed. Examples of soluble metal salts that dissolve to produce cationic metal catalyst, including iron-containing salts, are described in U.S. Pat. Nos. 5,958,288 and 5,980,775, the entireties of these documents being incorporated herein by reference. Exemplary iron cation catalyst may be provided in a CMP slurry in the form of an iron salt that is soluble in a liquid (e.g., aqueous) carrier. The salt may be a ferric (iron III) or ferrous (iron II) compound such as iron nitrate, iron sulfate, an iron halide (including fluoride, chloride, bromide, iodide, as well as perchlorates, perbromates, and periodates), or an organic iron compound such as an iron acetate, acetylacetonate, citrate, gluconate, malonate, oxalate, phthalate, succinates, etc.
Also, commonly, a stabilizer is included with the metal cation to control the amount of free metal cation in the composition, thereby deliberately subduing the effect of the catalyst to a desired degree. See, e.g., U.S. Pat. Nos. 5,980,775 and 6,068,787. The stabilizer can form a complex with the metal cation to reduce its reactivity by a desired amount. Examples of stabilizers used in past CMP slurries include phosphoric acid, phthalic acid, citric acid, malonic acid, phosphonic acid, oxalic acid, and others.
When processing a surface that includes both tungsten and non-tungsten (e.g., oxide) materials, various performance features are highly important for efficiently producing high quality processed substrates. A high removal rate for tungsten is required for good processing throughput. Also highly desirable is a high ratio of the removal rate of tungsten compared to the oxide, sometimes referred to as “tunability or “selectivity.” A slurry that provides exceptional removal properties (removal rates, selectivity) of tungsten and oxide can produce processed substrates that are said to exhibit excellent “topography” (described in more detail below), which is necessary for producing high quality devices from the processed substrate. But, removal properties must be balanced with other performance factors, such as the tendency of some CMP processing chemicals to cause corrosion of tungsten, specifically, to cause corrosion of tungsten plug structures. High levels of corrosion reduce the quality of a processed substrate by increasing the level of defects in devices prepared from the substrate. High corrosion rates have been correlated to high static etch rates of a slurry.
As a more general matter, a commercial CMP slurry product should exhibit a high level of stability during preparation, extended storage, transport, and use. A stable slurry is one that does not unduly separate or settle during storage (e.g., by settling of suspended abrasive particles), does not exhibit undue particle size growth during storage, and does not exhibit undue particle size growth during use, which would increase the level of defects (especially scratches) present at a surface of a processed substrate.
A processed substrate must exhibit excellent topography. In a processed substrate having a surface made of a combination of metal and oxide materials, topography characteristics include physical phenomena referred to as “erosion” of oxide, “dishing” of the metal, and their combined effect, which is referred to as “step height.” In one type of substrate surface pattern commonly referred to as a line and space (L&S) pattern, a surface includes line fields and spaces. The line fields, or patterned fields, include line arrays of metal and oxide. The line fields are distributed among fields (spaces) of continuous dielectric material. The line arrays include metal and oxide lines, such as lines of tungsten and silicon oxide, and may be of any density or size, for example alternating 1 micron-wide lines of metal and 1 micron-wide lines of oxide, i.e., a 50% 1 micron array, or alternating lines of different size or density, for example of 1 micron-wide lines of metal and 3 micron-wide lines of oxide, i.e., a 25% 1×3 micron array. The fields of continuous dielectric material, for comparison, may typically be larger in dimension, and have a surface of continuous dielectric material such as a silicon oxide, for example TEOS. An exemplary field (or “space”) of continuous dielectric material can be a 100 um×100 um area.
To evaluate post-polishing pattern performance of such line and space substrates, the absolute oxide loss (material removed) that occurs at the continuous dielectric field is determined, such as by an optical method using commercially available equipment. The continuous dielectric field is used as a reference for the relative pattern measurements in the arrays. For example, a line array comprised of alternating tungsten metal and TEOS oxide lines can be measured by profilometry or AFM with respect to the continuous field oxide. Erosion is characterized as a difference in the relative height of the oxide, such as the 1 micron TEOS lines, in the line array, as compared to the continuous field oxide. A positive erosion value is interpreted as relative recess of the oxide lines as compared to the continuous field oxide. Metal dishing typically refers to the relative height of the metal lines as compared to the oxide lines in the line array. For example in the 50% 1×1 micron line array, a value of 200 Angstroms dishing is interpreted as 200 Angstrom recess of the tungsten lines relative to the oxide lines. Adding the erosion and the dishing provides the total step height, in this case from the recessed (dished tungsten) to the field oxide. Total oxide or metal loss in the array can be determined by combining the dishing and erosion values with the absolute oxide loss values determined for the continuous field.
Yet another topography defect is known as a protrusion of one feature (e.g., a metal structure) relative to an adjacent feature (e.g., an insulating structure). A protrusion can be, for example, a portion of a metal (tungsten) feature that, after CMP processing (e.g., polishing), has a height that extends (protrudes) above an upper surface of an adjacent dielectric (e.g., oxide) layer. I.e., portions of metal features of a processed substrate surface may protrude above adjacent dielectric materials. Protrusions can result in a defective product prepared from the processed substrate, and, if present, may require an extra processing step to be removed.
Preferred commercial CMP polishing processes can be effective to remove metal (e.g., tungsten) from a substrate surface that also contains non-metal (e.g., dielectric), without producing unacceptable erosion, dishing, or protrusions; without undue corrosion of metal structures; and with low levels of defects such as scratches and residue present at the processed surface. Preferred processes can exhibit a high removal rate for the metal and good selectivity of the metal relative to the non-metal material. CMP compositions useful in these processes can preferably be stable during storage.
There is ongoing need in the semiconductor processing industry for CMP slurries useful for processing (e.g., polishing) tungsten-containing substrates, that provide useful or improved performance in areas of: removal rates and selectivity in removing tungsten and oxide materials; reduced topography defects including dishing, erosion, and protrusion; and useful or advantageous (i.e., low) levels of tungsten corrosion.